Although the biosynthetic pathways giving rise to the major phospholipid structures in Escherichia coli have been defined, the mechanisms by which total phospholipid synthesis is regulated and coordinated with other cellular processes remains basically unknown. The fundamental goal of this proposal is to identify the site(s) responsible for the regulation of phospholipid synthesis on the basis of in vivo experiments that measure the levels of lipid biosynthetic intermediates followed by in vitro analysis to confirm the identity of the regulated protein. The basic hypothesis that will serve as a point of departure to realize this goal is that acyl carrier protein is the regulatory site. The central position in lipid biosynthesis occupied by acyl carrier protein and its ability to be metabolically interconverted between active and inactive forms are features that make this protein a prime candidate for the regulatory site. The mechanisms that operate to coordinate cellular events have proven difficult to isolate during balanced growth, but are somewhat easier to analyze when the system is perturbed. Therefore, our approach will be to study the regulation of phospholipid synthesis in physiologically imbalanced systems. These include the study of acyl carrier protein gene expression and turnover in strains possessing increased acyl carrier protein gene dosage and during general metabolic shiftdowns that result in the downregulation of phospholipid synthesis. Our recent advances in procedures for the analysis of the acyl carrier protein pool composition in vivo and in cloning the acyl carrier protein gene make these experiments a feasible undertaking. The results of these experiments should provide valuable information on the coordination of phospholipid and macromolecular synthesis.